Title: Influence of demodulation bandwidth on demodulation spectrum of ship radiated noise

Author(s): CHENG Yusheng; WANG Sen; DING Chao; LIU Qijun

Affiliation(s): Navy Submarine Academy

Abstract: A mathematical model of amplitude-modulated ship radiated broadband noise signal is established making use of the principle of Fourier decomposition, and a mathematical expression for demodulation spectrum of ship radiated noise is derived by the square demodulation algorithm. The two following new conclusions from analysis of the demodulation spectrum are obtained by means of theoretical analysis and simulation calculation: (1) the relationship between demodulation performance and demodulation processing bandwidth: when the modulation depths of different frequency bands of ship radiated noise received by the sonar are equal, the demodulation performance is positively proportional to bandwidth of the band-pass filter used for demodulation, and the wider the band-pass filter bandwidth is, the higher the signal-to-noise ratio (SNR) of the demodulation spectrum is; (2) the relationship between broadband demodulation spectrum and sub-band demodulation spectrum: the broadband demodulation spectrum of the ship radiated noise can be approximately regarded as a sum of different sub-band demodulation spectrums. In order to verify the two conclusions above, the demodulation spectrum of actual ship radiated noise is processed correspondingly, and the result is consistent with the simulation.